Not Applicable.
Not Applicable.
The present invention relates in general to monitoring the position of fluid valves, and, more specifically, to a manner of interconnecting a position sensing switch to a movable element of a valve.
Fluid valves are important components of modern industrial control and manufacturing systems. For example, they are used in controlling the application of pressurized air to pneumatically-operated machines such as presses and other machine tools. It is often desirable or necessary to monitor the position of automatically controlled valves to ensure that a particular valve proper actuates and deactuates appropriately. Monitoring may also be necessary to ensure the safety of the human operators. A monitoring signal may be used to generate a visual or audible indication of a malfunctioning valve, may be used to automatically deactivate system operation in response to a fault, or both.
Many different types of sensing technologies have been used for monitoring valve position. Magnetic sensors have been used wherein a movable valve element is configured to affect a magnetic field at a predetermined sensing location as the valve element moves between an actuated and a deactuated position. The magnetic field can be generated by a permanent magnet (either moving or stationary) or by an electromagnet. A magnet sensor has the advantage of having minimal interference with operation of the movable valve element, but has the disadvantage of being relatively expensive compared to other sensing technologies.
Pressure switches have also been used to monitor valve performance. Assuming a source of pressurized fluid (e.g., air) is present, then the position of a valve element can be monitored by detecting the presence of pressurized fluid in the outlet of the valve, for example. Pressure switches can be accommodated with essentially any kind of valve without affecting the design of the moving elements, but to they are also relatively expensive.
One of the more cost-effective sensing technologies has been the use of electric sensing switches wherein an electric switch is mechanically connected to the valve so that the conduction state of the switch is determined according to the position of the valve element. If a failure occurs in the switch, however, a false monitoring signal can be generated such that the valve is not in the same actuated or deactuated state that is currently being indicated by the monitoring signal. Potential switch failures include switch contacts that have welded shut and a broken return spring. Impacts of a moving valve component against the switch during each operating cycle of the valve have resulted in excessive wear, leading to these and other kinds of switch failures.
The present invention has the advantage of eliminating a main source of switch failures in electronic sensing switches for monitoring valve performance.
In one aspect of the invention, a monitored fluid control valve is provided having a valve body with an elongated bore. A movable valve element is slidably received in the bore. A switch assembly has an aperture aligned with the bore. The switch assembly includes an electrical switch having a switch arm operatively connected to switch contacts for driving the switch contacts between an open state and a closed state. The switch arm is linked to the movable valve element so that the switch arm is directly driven to match linear reciprocation of the movable valve element.